As is known, display devices having a microdisplay, such as for example those based on OLEDs (organic light-emitting diodes), comprise an active zone formed from a matrix of pixels and an electrical connection zone which is placed so as to be adjacent this active zone and which typically comprises an alignment of electrical contacts. These microdisplay devices are fabricated by assembling optical color filters respectively on color dots of the pixels that form the active part of the microdisplay and that cover a semiconductor substrate, typically consisting of a silicon wafer. These filters are usually deposited on the internal face of a glass sheet which is bonded to the microdisplay so as to protect it, in the manner of an impermeable encapsulation, from the moisture and oxygen of the outside environment.
In general, this assembly is produced by applying an ultraviolet-crosslinkable adhesive film over the entire surface of the microdisplay or of the internal face of the protective sheet equipped with the filters, because it is technically difficult to apply this adhesive just to the active zone of the microdisplay. Now, as a result of bonding the protective sheet to the microdisplay and of crosslinking the adhesive by UV radiation through the sheet thus assembled, there is some cured adhesive covering the electrical contacts of the connection zone, thereby complicating the subsequent operation of “liberating” the contacts by cutting the sheet in line with the point of separation between the active zone and the connection zone.
To solve this problem of preserving the electrical contacts of the microdisplay thus covered with the protective sheet, in the past this crosslinkable adhesive has been especially applied:                in the form of a bead surrounding the active zone of the microdisplay as for example described in the document U.S. Pat. No. 6,825,612, with the resulting drawback that the microdisplay is imperfectly protected by the sheet; or        selectively on this active zone by screen printing, which has the drawback of requiring a high degree of precision in applying the spots of adhesive; or        by prestructuring the assembly face of the protective sheet in order to form therein cavities intended to face the electrical contacts and having a depth very much greater than the thickness of the applied adhesive film, so that the adhesive is lodged in these cavities, with as drawback the required prior step of structuring the sheet.        
Document WO-A-2007/005228 provides a method of assembling a protective sheet provided with extensions or feet to be bonded to a microdisplay, this method comprising, in succession:                application of adhesive in the form of beads at the interface between these extensions of the sheet and the microdisplay;        deposition, on the external sides of these extensions, of a photosensitive resin of the Kapton® type followed by an inorganic sealing layer, especially one covering this resin; and then        dissolution of this resin and of that part of the inorganic layer covering said resin, so as in the end to obtain only that part of said layer which is located over the thickness of the beads of adhesive and necessary for sealing the assembly.        
A major drawback of the method described in the above document lies in the difficulty of implementing it due especially to the extensions of the protective sheet and to the required precision in applying the adhesive and the photosensitive resin along these extensions.